1. Field of the Invention
This invention relates to an outboard motor steering system.
2. Description of the Related Art
One example of a conventional outboard motor steering system that uses an actuator such as an electric motor to regulate the steering angle of an outboard motor can be found in Japanese Laid-Open Patent Application No. Hei 5(1993)-221385. In this technique, electric power consumption is reduced by supplying less drive current to an actuator during non-steering than during steering.
In the outboard motor steering system, when the engine speed of the outboard motor is raised to increase the thrust produced by the propeller, the steering load is increased owing to higher water resistance. In addition, as the thrust grows larger, the speed (particularly the water speed) of the boat rises to increase the water pressure acting on the rudder section of the outboard motor, thus further increasing the steering load.
The usual practice is therefore to supply an adequately large amount of drive current to the steering actuator so as to enable stable steering when the steering load becomes large. When this is done, however, the amount of drive current supplied to the steering actuator during low-speed cruising (when the steering load is small) becomes larger than necessary. Room for power conservation therefore remains.
Moreover, when drive current is supplied in such a large amount that the actuator output becomes excessive relative to the steering load, the change in steering angle overshoots the desired steering angle. This degrades the steering convergence property and has a bad effect on steering performance.